Thermal transfer image-receiving sheet

Abstract: A thermal transfer image-receiving sheet comprising a substrate sheet, a dye-receptive layer provided on one surface of the substrate sheet and a dye-unreceptive layer provided on the other surface of the substrate sheet, the dye-unreceptive layer comprising a composition composed mainly of at least one thermoplastic resin having at least one reactive functional group and an isocyanate compound or a chelate compound. A thermal transfer image-receiving sheet comprising a substrate sheet (1), a dye-receptive layer (2) provided on one surface of the substrate sheet and a dye-unreceptive layer (3) provided on the other surface of the substrate sheet, the dye-unreceptive layer comprising a release agent which is the same as that contained in the dye-receptive layer or does not migrate to other places, for example, comprises an amino-modified silicone and an epoxy-modified silicone or a product of a reaction of both of them, or an addition-polymerizable silicone or a cured product obtained by a reaction thereof. A thermal transfer image-receiving sheet comprising a substrate sheet, a dye-receptive layer provided on one surface of the substrate sheet and a lubricious back surface layer provided on the other surface of the substrate sheet, the lubricious back surface layer being composed mainly of a binder and a nylon filler.

Description: The present invention relates to a thermal transfer image-receiving sheet which is receptive to a dye transferred from a thermal transfer sheet by heating, which thermal transfer image-receiving sheet can be widely utilized in the field of various color printers including video printers. In recent years, a system where video images, TV images and still images, such as computer graphics, are directly printed as a full color image has advanced, which has led to a rapid expansion of the market thereof. Among others, a system which has attracted attention is such that a sublimable dye as a recording material is put on an image-receiving sheet and heated by means of a thermal head in response to recording signals to transfer the dye onto the image-receiving sheet, thereby forming a recorded image. In this recording system, since a dye is used as the colorant, the sharpness is very high and, at the same time, the transparency is excellent, so that it is possible to provide an image having excellent reproduction and gradation of intermediate colors equivalent to those of an image formed by the conventional full color offset printing and gravure printing. In this case, the formed image has a high quality comparable to photographic images. Printers in current use in the above thermal transfer system are mainly of such a type that a thermal transfer image-receiving sheet is automatically carried to a thermal transfer section within a printer and, after printing, automatically delivered from the printer. Further, in order to carry out overlap printing of three colors or four colors, it is a common practice to provide a detection mark on the thermal transfer image-receiving sheet in its image-unreceptive surface, that is, the back surface, located opposite to the image-receiving surface for the purpose of preventing the occurrence of a shear in the printing position of each color. Not only the construction of the thermal transfer sheet but also the construction of the image-receiving sheet on which an image is to be formed is important to the practice of the above thermal transfer method with a high efficiency. In particular, the properties of the image-unreceptive surface (back surface) located opposite to the image-receptive surface of the thermal transfer image-receiving sheet are important for smoothly carrying out automatic feed and delivery of the thermal transfer image-receiving sheet. For example, when the image-receiving sheets with an image being formed thereon are put on top of another for storage, the dye on the print surface migrates to the back surface of another thermal transfer image-receiving sheet in contact with the print surface to remarkably stain the back surface, which deteriorates the appearance. Further, in this case, the color of the print surface is partly or entirely dropped out, or restaining occur. Furthermore, in domestic use, a back surface free from a detection mark as in photographic paper is preferred from the viewpoint of appearance. However, when no detection mark is provided, it is difficult to distinguish the image-receptive layer from the back surface. When the thermal transfer image-receiving sheet is set in a printer in such a state that the image-receiving surface and the back surface are inversive, the erroneous setting cannot be detected by the printer and the printer begins to print. If that happens, in the conventional thermal transfer image-receiving sheet, fusing between the thermal transfer sheet and the back surface of the thermal transfer image-receiving sheet occurs within the printer, which inhibits the thermal transfer image-receiving sheet from being delivered from the printer, so that the printer should be sent to a maker for repair. The provision of a dye-receptive layer on both surfaces of the substrate sheet is considered as a means for solving the problem of heat fusing of the back surface. In this case, however, when prints are put on top of one another for storage, the dye migrates to cause problems of a lowering in image density, staining of contact surface, restaining and the like. Furthermore, since the dye-receptive layer comprises a dyeable resin and is even, the image-receptive layers are likely to come into close contact with each other, which, also in the stage before printing, results in a problem of a failure in automatic feed such as a problem that a plurality of image-receiving sheets are carried together in an overlapped state in a feeder of a printer. For example, even though a filler is added to the image-receptive layer for the purpose of preventing the occurrence of this problem, the highlight portion of the print is likely to become unsharp. Another means for solving the above problem is to add a release agent to the back surface layer as a dye-unreceptive layer. However, if the release agent is added in an amount sufficient to impart satisfactory releasability, the releasing component contained in the back surface layer is transferred to the image-receptive surface when the back surface layer is put on top of the image-receptive surface, which unfavorably raises problems of occurrence of a failure in printing such as partial dropout in the print portion and uneven print density, a lowering in coefficient of dynamic friction between the image-receptive surface of the image-receiving sheet and the transfer agent surface of the thermal transfer sheet, which is causative of the occurrence of a shear in the printing position of each color. Further, in this case, the releasing component contained in the back surface layer migrates to a feed and delivery mechanism, such as a paper feed rubber roller, and a platen rubber roller in a printer, which gives rise to a change in coefficient of friction of these members, so that troubles are likely to occur such as a failure in feed and delivery of sheets and oblique carrying of the image-receiving sheet. A thermal transfer receiver sheet having a back-coat comprising a cross-linked polymer matrix is disclosed in EP-A-0 541 266, in which N-(alkoxymethyl) amine resins such as alkoxymethyl derivatives of urea, guanamine and melamine resins are disclosed as the cross-linking agents used. EP-A-0 545 710 discloses a thermal transfer dye image-receiving sheet having a back surface coating layer comprising silicone block copolymer resins, silicon oils, silicone varnishes, fluorine compounds, phosphate ester compounds or fatty acid ester compounds. Accordingly, an object of the present invention is to solve the above problems of the prior art and to provide a thermal transfer image-receiving sheet having excellent service properties for use in a thermal transfer system where a sublimable dye is used, which thermal transfer image-receiving sheet hardly causes a lowering in print density and migration of dye to the back surface of the image-receiving sheet when a plurality of image-receiving sheets are put on top of another for storage, can be delivered from the printer without fusing to the thermal transfer sheet by virtue of excellent releasability of the back surface even though printing is carried out on the thermal transfer image-receiving sheet with the image-receiving surface and the back surface being inversive and is free from an adverse effect of the release agent added to the back surface layer on the image-receiving surface and substantially free from the migration of the release agent to a sheet feed and delivery mechanism and a platen rubber roller. The present inventors have made extensive and intensive studies with a view to solving the above problems, which has led to the completion of the present invention. Specifically, according to the present invention, there is provided a thermal transfer image-receiving sheet comprising a substrate sheet, a dye-receptive layer provided on one surface of said substrate sheet and a dye-unreceptive layer provided on the other surface of said substrate sheet, the dye-unreceptive layer comprising a reaction product of (a) at least one thermoplastic resin having at least one reactive functional group and (b) an isocyanate compound or a chelate compound. Fig. 1 is a cross-sectional view of an embodiment of the thermal transfer image-receiving sheet according to the present invention; Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. A typical cross-sectional view of an embodiment of the thermal transfer image-receiving sheet according to the present invention is shown in Fig. 1. This thermal transfer image-receiving sheet comprises a substrate sheet 1, a dye-receptive layer 2 provided on one surface of the substrate sheet and a dye-unreceptive layer 3 as a back surface provided on the other surface of the substrate sheet, characterized in that the dye-unreceptive layer 3 comprises a composition composed mainly of at least one thermoplastic resin having at least one reactive functional group and an isocyanate compound or a chelate compound. Materials for constituting each layer of the thermal transfer image-receiving sheet of the present invention will now be described. 1) Substrate sheet In the present invention, materials usable in the substrate sheet include papers. Any of various papers per se, converted papers and other types of papers may be used, and examples thereof include wood free paper, coated paper, art paper, cast coated paper and fiber board and other types of papers such as paper impregnated with an resin emulsion, a synthetic rubber latex or the like and paper containing an internally added synthetic resin. Further, a laminated paper comprising the above paper and various plastic films may also be used. When synthetic paper is used, polystyrene synthetic paper, polyolefin synthetic paper and the like are preferred. Examples of the plastic film include a polyolefin resin film, a hard polyvinyl chloride film, a polyester resin film, a polystyrene film, a polycarbonate film, a polyacrylonitrile film and a polymethacrylate film. These plastic films are not particularly limited, and use may be made of not only transparent films but also a white opaque film or an expanded film prepared by adding a white pigment or filler to the above synthetic resin and forming a film from the mixture or expanding the mixture. The above materials may be used alone. Alternatively, as described above in connection with paper, they may be used as a laminate comprising a combination thereof with other materials. Further, in the formation of a dye-receptive layer or a dye-unreceptive layer (a back surface layer) on the above substrate sheet, it is also possible to conduct a corona discharge treatment or provide a primer coating or an intermediate layer according to need. The thickness of the substrate sheet is in the range of from about 10 µm to 400 µm, preferably in the range of from 100 to 300 µm. 2) Dye-receptive layer In the thermal transfer image-receiving sheet of the present invention, the dye-receptive layer is not particularly limited and may be any known dye-receptive layer commonly used in the sublimation thermal dye transfer system. For example, the following materials may be used. (i) Resins having an ester bond Polyester resins, polyacrylic ester resins, polycarbonate resins, polyvinyl acetate resins, styrene acrylate resins, vinyltoluene acrylate resins and the like. (ii) Resins having a urethane bond Polyurethane resins and the like. (iii) Resins having an amide bond Polyamide resins and the like. (iv) Resins having a urea bond Urea resins and the like. (v) Other resins having a high polarity Polycaprolactone resins, styrene/maleic anhydride resins, polyvinyl chloride resins, polyacrylonitrile resins and the like. In addition to the above synthetic resins, mixtures or copolymers thereof may also be used. In the thermal transfer, the dye-receptive layer is brought in contact with a thermal transfer sheet, and the laminate is pressed with heating by means of a thermal head or the like, so that the dye-receptive layer is likely to stick to the surface of the thermal transfer sheet. For this reason, in the formation of the dye-receptive layer, a releasing agent permeable to a dye is generally incorporated into the above resin. Solid waxes, fluorine or phosphoric ester surfactants, silicone oils may be used as the release agent. Although the silicone oils may be in an oil form, reaction-curable silicone oils are preferred. For example, a combination of an amino-modified silicone with an epoxy-modified silicone is preferred. The amount of the release agent added is 5 to 50% by weight, preferably 10 to 20% by weight, based on the weight of the resin when the release agent is solid wax, and 0.5 to 10% by weight based on the resin when the release agent is a fluorine or phosphoric ester surfactant. The curable silicone oils may be used in a large amount because they are not sticky, and the amount of the curable silicone oils added may be in the range of from 0.5 to 30% by weight based on the amount of the resin. In all the above release agents, when the amount is excessively small, the releasing effect becomes unsatisfactory. On the other hand, when the amount is excessive, the receptivity to a dye is lowered, so that insufficient recording density and other adverse effects occur. Regarding the method for imparting releasability to the dye-receptive layer, besides the above-described incorporation of a release agent into the dye-receptive layer, it is also possible to separately provide a release layer on the dye-receptive layer. Further, if necessary, the dye-receptive layer may contain inorganic fillers such as finely divided silica. The dye-receptive layer is formed by dissolving or dispersing the above-described materials for constituting the dye-receptive layer in a solvent to prepare a coating solution, coating the coating solution by gravure reverse coating or other coating methods and drying the resultant coating. In this case, the coverage may be in the range of from 1.5 to 15 g/m 2 , preferably in the range of from 1.5 to 6.0 g/m 2 . 3) Dye-unreceptive layer (back surface layer) The thermal transfer image-receiving sheet according to the present invention is characterized by the dye-unreceptive layer (back surface layer). By virtue of the provision of the dye-unreceptive layer, the thermal transfer image-receiving sheet causes no staining of the back surface layer with a dye even when a plurality of image-receiving sheets after printing are put on top of one another for storage, has an excellent suitability for automatic feeding and can be delivered from the printer without fusing to a thermal transfer sheet by virtue of excellent releasability of the back surface even though it is fed into the printer with the back surface and the image-receiving surface being inversive. For attaining the above properties, the dye-unreceptive layer comprises a composition composed mainly of at least one thermoplastic resin having at least one reactive functional group, preferably at least one vinyl resin having a hydroxyl group and an isocyanate compound or a chelate compound. If necessary, it may further comprise any one or both of an organic and/or inorganic filler and a release agent. Furthermore, other thermoplastic resins may also be added for the purpose of improving the productivity and gloss in such an amount as will not be detrimental to the performance of the dye-unreceptive layer. The regulation of the hydroxyl value in the vinyl resin is easier than that in polyester resins, polyolefin resins and polycarbonate resins and other resins, so that the degree of crosslinking can be easily controlled as desired, which enables the above-mentioned staining of the back surface caused by the migration of the dye to be easily prevented. Also from the viewpoint of production stability, the vinyl resin wherein the hydroxyl value can be easily regulated is preferred by taking into consideration easy optimization of the solubility in the solvent used, the pot life of the isocyanate compound or chelate compound, which is generally unstable against water, and the like. Preferred examples of the vinyl resin include polyvinyl alcohol resin, polyvinyl formal resin, polyvinyl acetoacetal resin, polyvinyl butyral resin and vinyl chloride/vinyl acetate/polyvinyl alcohol copolymer resin. High Tg and hydrophilicity are desired from the viewpoint of resistance to staining with a dye, and the regulation of solubility in general-purpose solvents and viscosity are required from the viewpoint of production stability. For this reason, the polyvinyl butyral resin is particularly preferred. Examples of the thermoplastic resin used in the present invention include vinyl resins, such as polyvinyl alcohol resins, polyvinyl acetate resins, polyvinyl chloride resins, vinyl chloride/vinyl acetate copolymer resins, acrylic resins, polystyrene resins, polyvinyl formal resins, polyvinyl acetoacetal resins and polyvinyl butyral resins, cellulosic resins, polyester resins and polyolefin resins. Thermoplastic resins having a reactive functional group and a low dyeability with a sublimable dye are used. The isocyanate compound may be any of an aromatic isocyanate and an aliphatic isocyanate, and the amount of the isocyanate compound added is preferably equal to or twice the amount of the reactive functional group of the thermoplastic resin having a reactive functional group. The chelate compound may be a titanium chelate compound, a zirconium chelate compound, an aluminum chelate compound or the like. Chelate compounds having a high curing activity are preferred. The amount of the chelate compound added is 25 to 300 parts by weight based on 100 parts by weight of the thermoplastic resin having a reactive functional group. Fillers used in the present invention are not particularly limited, and examples thereof include polyethylene wax, bisamides, polyamides, such as nylon, acrylic resins, crosslinked polystyrene, silicone resins, silicone rubbers, talc, calcium carbonate and titanium oxide. Fillers capable of improving the lubricity are preferred, and the particle diameter is suitably in the range of from 2 to 15 µm. Among the above materials, nylon 12 filler is particularly preferred from the viewpoint of resistance to offset of dye, that is, staining resistance, and good lubricity. The amount of the filler added may be in the range of from 0 to 200 parts by weight based on 100 parts by weight in total of the thermoplastic resin and the release agent. In the present invention, various surfactants, silicon compounds, fluorine compounds and other compounds may be used as the release agent. Among them, silicon compounds are preferred. Three-dimensional crosslinked silicones and reactive silicone oils are preferred from the viewpoint of avoiding the migration to other places. The reactive silicone oil is particularly preferred because the use thereof in a small amount can provide a sufficient releasability and there is no fear of the release agent migrating to other places. The silicone oil may be added in an oil form to the resin for constituting the dye-unreceptive layer, coated in a sufficiently dispersed state, dried and then crosslinked. Further, when the reactive silicone oil reacts with an isocyanate compound or a chelate compound as the curing agent for the thermoplastic resin, thereby causing the reactive silicone oil to be fixed to the resin, the fear of the migration can be completely eliminated. Specific preferred examples of the reactive silicone include an amino-modified silicone and an epoxy-modified silicone and a cured product obtained by a reaction thereof, an addition-polymerizable silicone and a cured product obtained by a reaction thereof, and a radiation-curable silicone and a cured product obtained by a reaction thereof. Further preferred examples of the reactive silicone include a hydroxyl-modified silicone oil and a carboxyl-modified silicone oil having an active hydrogen which can be cured when used in combination with an isocyanate compound or a chelate compound. The amount of the release agent added is suitably in the range of from 0 to 5 parts by weight based on 100 parts by weight of the thermoplastic resin. In working examples which will be described later, wire bar coating was used for the formation of the dye-unreceptive layer (back surface layer) by coating from the viewpoint of convenience. However, the coating method is not particularly limited and may be freely selected from gravure coating, roll coating, blade coating, knife coating, spray coating and other conventional coating methods. The thermal transfer image-receiving sheet according to the present invention comprises a substrate sheet, a dye-receptive layer provided on one surface of said substrate sheet and a dye-unreceptive layer provided on the other surface of said substrate sheet, the dye-unreceptive layer comprising a composition composed mainly of at least one thermoplastic resin having at least one reactive functional group, preferably a vinyl resin having a hydroxyl group, and an isocyanate compound or a chelate compound. The adoption of such a constitution brings the thermoplastic resin of the dye-unreceptive layer as a back surface layer of the image-receiving sheet to a crosslinked structure, which contributes to an improvement in heat resistance. This improves the suitability of the image-receiving sheet for automatic feed and delivery in a printer. Further, the sublimable dye receptivity of the dye-unreceptive layer in the image-receiving sheet can also be lowered, so that the stain of the back surface with a sublimable dye can be reduced even when a plurality of sheets are stored with the surface of the print facing the back surface. Further, in the thermal transfer image-receiving sheet according to the present invention, the thermoplastic resin of the dye-unreceptive layer as the back surface may be a thermoplastic resin having a hydroxyl group as the reactive functional group, more specifically, polyvinyl formal, polyvinyl acetoacetal or polyvinyl butyral. This embodiment enables the thermoplastic resin to be more surely reacted, so that the above effect can be attained more efficiently and stably. Furthermore, in the thermal transfer image-receiving sheet according to the present invention, the dye-unreceptive layer provided in the back surface may further comprise an organic filler and/or an inorganic filler or a release agent, or an organic filler and/or an inorganic filler and a release agent. According to this embodiment, the above effect can be further improved. Specifically, curing of the binder resin contributes to an improvement in heat resistance, and the addition of the release agent in the minimum required amount contributes to a further improvement in releasability and lubricity of the back surface of the thermal transfer image-receiving sheet. Further, since the release agent is fixed to the dye-unreceptive layer, it is not transferred to other places. Therefore, the automatic feed and delivery of the image-receiving sheet in a printer becomes more smooth. Furthermore, even though the thermal transfer sheet is fed into a printer with the back surface and the image-receiving surface of the image-receiving sheet being inversive and, in this state, printing is carried out, the sheet can be successfully delivered from the printer without the occurrence of heat fusing or sticking between the thermal transfer sheet and the back surface of the image-receiving sheet. In the thermal transfer image-receiving sheet according to the present invention, the nylon filler added to the back surface layer is a nylon 12 filler. The nylon 12 filler is superior to nylon 6 and nylon 66 in water resistance and less likely to absorb water, so that under high-temperature and high-humidity conditions it gives rise to no change in properties and can stably exhibit the above properties. Further, in the thermal transfer image-receiving sheet according to the present invention, the nylon filler may be spherical and have a molecular weight in the range of from 100,000 to 900,000. This embodiment contributes to a further improvement in lubricity and blocking resistance of the back surface of the image-receiving sheet and an improvement in abrasion resistance of the filler. Therefore, there is no possibility that powder generated by abrasion is adhered to the rubber roller and the like and damages the rubber roller and other counter materials. Furthermore, in the thermal transfer image-receiving sheet according to the present invention, the nylon filler may have an average particle diameter in the range of from 0.01 to 30 µm. This embodiment prevents the nylon filler from being buried in the back surface layer or prevents excessive protrusion of the nylon filler from the back surface layer which enhances the coefficient of friction or causes falling of the filler, so that the contemplated properties can be stably attained. Example A1 Synthetic paper (Yupo FPG#150 having a thickness of 150 µm; manufactured by Oji-Yuka Synthetic Paper Co., Ltd.) was used as a substrate sheet, and a coating solution having the following composition for a dye-receptive layer was coated by wire bar coating on one surface of the synthetic paper so that the coverage on a dry basis was 5.0 g/m 2 , and the resultant coating was dried. A coating solution having the following composition for a dye-unreceptive layer (a back surface layer) was coated on the other surface of the substrate sheet in the same manner as described above so that the coverage on a dry basis was 1.0 g/m 2 , and the resultant coating was dried, thereby providing a thermal transfer image-receiving sheet of Example A1. Composition of coating solution for dye-receptive layer 1 ○ Polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) 100 parts by weight 2 ○ Release agent Amino-modified silicone (KF-393 manufactured by The Shin-Etsu Chemical Co., Ltd.) 5 parts by weight Epoxy-modified silicone (X-22-343 manufactured by The Shin-Etsu Chemical Co., Ltd.) 5 parts by weight 3 ○ Solvent (methyl ethyl ketone/toluene; weight ratio = 1 : 1) 500 parts by weight Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl alcohol (C-25 manufactured by The Shin-Etsu Chemical Co., Ltd.) 100 parts by weight 2 ○ Chelate compound (Orgatix ZB-110 manufactured by Matsumoto Trading Co., Ltd.) 25 parts by weight 3 ○ Water 900 parts by weight Example A2 A thermal transfer image-receiving sheet of Example A2 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl formal (Denka Formal #200 manufactured by Denki Kagaku Kogyo K.K.) 100 parts by weight 2 ○ Release agent Amino-modified silicone (KF-393 manufactured by The Shin-Etsu Chemical Co., Ltd.) 2 parts by weight Epoxy-modified silicone (X-22-343 manufactured by The Shin-Etsu Chemical Co., Ltd.) 2 parts by weight 3 ○ Isocyanate compound Coronate 2030 manufactured by Nippon Polyurethane Industry Co., Ltd. 300 parts by weight 4 ○ Solvent Isopropyl alcohol/ethyl acetate; weight ratio = 1 : 1 900 parts by weight Isopropyl alcohol will be hereinafter referred to as "IPA." Example A3 A thermal transfer image-receiving sheet of Example A3 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (Denka Butyral #2000-L manufactured by Denki Kagaku Kogyo K.K.) 100 parts by weight 2 ○ Release agent Carboxyl-modified silicone (X-22-3710 manufactured by The Shin-Etsu Chemical Co., Ltd.) 2 parts by weight 3 ○ Chelate compound (Orgatix AI-80 manufactured by Matsumoto Trading Co., Ltd.) 100 parts by weight 4 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Example A4 A thermal transfer image-receiving sheet of Example A4 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl acetoacetal (KS-1 manufactured by Sekisui Chemical Co., Ltd.) 100 parts by weight 2 ○ Release agent Hydroxy group-modified silicone (X-22-160B manufactured by The Shin-Etsu Chemical Co., Ltd.) 2 parts by weight 3 ○ Isocyanate compound (Coronate HX manufactured by Nippon Polyurethane Industry Co., Ltd.) 400 parts by weight 4 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Example A5 A thermal transfer image-receiving sheet of Example A5 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Vinyl chloride/vinyl acetate/polyvinyl alcohol copolymer (Eslec AL manufactured by Sekisui Chemical Co., Ltd.) 200 parts by weight 2 ○ Release agent Amino-modified silicone (KF-393 manufactured by The Shin-Etsu Chemical Co., Ltd.) 3 parts by weight Epoxy-modified silicone (X-22-343 manufactured by The Shin-Etsu Chemical Co., Ltd.) 3 parts by weight 3 ○ Chelate compound (Orgatix TC-200 manufactured by Matsumoto Trading Co., Ltd.) 400 parts by weight 4 ○ Solvent (methyl ethyl ketone/toluene/IPA; weight ratio = 1 : 1: 1) 800 parts by weight Methyl ethyl ketone will be hereinafter referred to as "MEK." Example A6 A thermal transfer image-receiving sheet of Example A6 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Vinyl chloride/vinyl acetate copolymer (Denka Vinyl #1000GK manufactured by Denki Kagaku Kogyo K.K.) 200 parts by weight 2 ○ Release agent Amino-modified silicone (KF-393 manufactured by The Shin-Etsu Chemical Co., Ltd.) 3 parts by weight Epoxy-modified silicone (X-22-343 manufactured by The Shin-Etsu Chemical Co., Ltd.) 3 parts by weight 3 ○ Isocyanate compound (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) 300 parts by weight 4 ○ Filler Talc 400 parts by weight 5 ○ Solvent (MEK/toluene; weight ratio = 1 : 1) 800 parts by weight Example A7 A thermal transfer image-receiving sheet of Example A7 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (BX-1 manufactured by Sekisui Chemical Co., Ltd.) 100 parts by weight 2 ○ Release agent Addition-polymerizable silicone (addition-polymerizable silicone B 2 parts by weight Catalyst (PL-50T manufactured by The Shin-Etsu Chemical Co., Ltd.) 1 part by weight 3 ○ Isocyanate compound (Coronate 2067 manufactured by Nippon Polyurethane Industry Co., Ltd.) 300 parts by weight 4 ○ Filler Polyethylene wax (SPRAY 30 manufactured by Sasol Co., Ltd.) 200 parts by weight 5 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Example A8 A thermal transfer image-receiving sheet of Example A8 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (BX-5 manufactured by Sekisui Chemical Co., Ltd.) 200 parts by weight 2 ○ Release agent Addition-polymerizable silicone (addition-polymerizable silicone B) 2 parts by weight Catalyst (PL-50T manufactured by The Shin-Etsu Chemical Co., Ltd. 1 part by weight 3 ○ Chelate compound (Orgatix TC-400 manufactured by Matsumoto Trading Co., Ltd.) 600 parts by weight 4 ○ Filler Nylon 12 filler (MW-330 manufactured by Shinto Paint Co., Ltd.) 40 parts by weight 5 ○ Solvent (MEK/toluene; weight ratio = 1 : 1) 800 parts by weight Comparative Example A1 A thermal transfer image-receiving sheet of Comparative Example A1 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl formal (Denka Formal #200 manufactured by Denki Kagaku Kogyo K.K.) 100 parts by weight 2 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Comparative Example A2 A thermal transfer image-receiving sheet of Comparative Example A2 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (Denka Butyral #2000-L manufactured by Denki Kagaku Kogyo K.K.) 100 parts by weight 2 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Comparative Example A3 A thermal transfer image-receiving sheet of Comparative Example A3 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Vinyl chloride/vinyl acetate copolymer (Eslec A manufactured by Sekisui Chemical Co., Ltd.) 200 parts by weight 2 ○ Filler Talc 400 parts by weight 3 ○ Solvent (MEK/toluene; weight ratio = 1 : 1) 800 parts by weight Comparative Example A4 A thermal transfer image-receiving sheet of Comparative Example A4 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (BX-1 manufactured by Sekisui Chemical Co., Ltd.) 100 parts by weight 2 ○ Filler Polyethylene wax (SPRAY 30 manufactured by Sasol Co., Ltd.) 200 parts by weight 3 ○ Solvent (IPA/ethyl acetate; weight ratio = 1 : 1) 900 parts by weight Comparative Example A5 A thermal transfer image-receiving sheet of Comparative Example A5 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (BX-5 manufactured by Sekisui Chemical Co., Ltd.) 200 parts by weight 2 ○ Filler Nylon 12 filler (MW-330 manufactured by Shinto Paint Co., Ltd.) 40 parts by weight 3 ○ Solvent (MEK/toluene; weight ratio = 1 : 1) 800 parts by weight Example A9 A thermal transfer image-receiving sheet of Example A9 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) 1 ○ Polyvinyl butyral (Denka Butyral #8000-1 manufactured by Denki Kagaku Kogyo K.K.) 40 parts by weight 2 ○ Chelate compound (Tenkarate TP-110 manufactured by Tenkapolymer K.K., Japan) 30 parts by weight 3 ○ Solvent (ethyl acetate/IPA; weight ratio = 1 : 1) 500 parts by weight Comparative Examples A6 and A7 A thermal transfer image-receiving sheet of Comparative Examples A6 and A7 was prepared in the same manner as in Example A1, except that the coating solution for a dye-unreceptive layer (a back surface layer) had the following composition. Composition of coating solution for dye-unreceptive layer (back surface layer) (Comparative Example A6) 1 ○ Polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) 100 parts by weight 2 ○ Isocyanate compound (Takenate A-14 manufactured by Takeda Chemical Industries, Ltd.) 20 parts by weight 3 ○ Solvent (methyl ethyl ketone/toluene; weight ratio = 1 : 400 parts by weight 1) (Comparative Example A7) 1 ○ Polyester resin (Vylon 600 manufactured by Toyobo Co., Ltd.) 100 parts by weight 2 ○ Chelate compound (Orgatix TC-400 manufactured by Matsumoto Trading Co., Ltd.) 150 parts by weight 3 ○ Solvent (methyl ethyl ketone/toluene; weight ratio = 1 : 1) 400 parts by weight Thus, the thermal transfer image-receiving sheets of Examples A1 to A9 of the present invention and Comparative Examples A1 to A7 were prepared. The following thermal transfer sheet was prepared as a thermal transfer sheet sample for use in a test for the evaluation of the performance of these thermal transfer image-receiving sheets in which test the thermal transfer image-receiving sheets were actually fed into a printer to form an image. (Preparation of thermal transfer sheet) A 6 µm-thick polyethylene terephthalate film having a back surface subjected to a treatment for rendering the surface heat-resistant was provided as a substrate sheet for a thermal transfer sheet, and an ink having the following composition for the formation of a thermal transfer layer was coated on the film in its surface not subjected to the treatment for rendering the surface heat-resistant by wire bar coating at a coverage on a dry basis of 1.0 g/m 2 . The resultant coating was dried to provide a thermal transfer sheet sample. Composition of ink for thermal transfer layer 1 ○ Cyan dye (Kayaset Blue 714, C.I. SOLVENT BLUE 63, manufactured by Nippon Kayaku Co., Ltd.) 40 parts by weight 2 ○ Polyvinyl butyral (Eslec BX-1 manufactured by Sekisui Chemical Co., Ltd.) 30 parts by weight 3 ○ Solvent (MEK/toluene; weight ratio = 1 : 1) 530 parts by weight (Test and results) The above thermal transfer sheet was used in combination with the thermal transfer image-receiving sheets of Examples A1 to A9 and Comparative Examples A1 to A7 to carry out a test for the following items, and the results are given in Table A1. 1) Releasability of back surface of image-receiving sheet (test on abnormal dye transfer to back surface of image-receiving sheet) The above-described thermal transfer sheet and the thermal transfer image-receiving sheets of Examples A1 to A9 and Comparative Examples A1 to A7 were put on top of the other in such a manner that the surface coated with an transfer ink of the thermal transfer sheet faced the surface of the dye-unreceptive layer (back surface) of the thermal transfer image-receiving sheet. A cyan image was recorded by means of a thermal head from the back surface (the surface which had been subjected to a treatment for rendering the surface heat-resistant) of the thermal transfer sheet under conditions of an applied voltage of 11 V, a step pattern in which the applied pulse width was successively reduced from 16 msec/line every 1 msec, and 6 lines/mm (33.3 msec/line) in the sub-scanning direction, and the releasability of the thermal transfer sheet from the back surface of the image-receiving sheet was observed. Criteria for evaluation : ○: Good releasability X: Poor releasability (occurrence of the capture of the ink layer of the thermal transfer sheet due to fusing or the like, the capture of the back surface layer of the image-receiving sheet, and other unfavorable phenomena) 2) Stain resistance of back surface of image-receiving sheet The above-described thermal transfer sheet and the thermal transfer image-receiving sheets of Examples A1 to A9 and Comparative Examples A1 to A7 were put on top of the other in such a manner that the surface coated with an transfer ink of the thermal transfer sheet faced the surface of the dye-receptive layer of the thermal transfer image-receiving sheet. A cyan image was formed on the surface of the dye-receptive layer in each image-receiving sheet by means of a thermal head from the back surface (the surface which had been subjected to a treatment for rendering the surface heat-resistant) of the thermal transfer sheet under conditions of an applied voltage of 11 V, a step pattern in which the applied pulse width was successively reduced from 8 msec/line every 0.5 msec, and 6 lines/mm (16 msec/line) in the sub-scanning direction. Thereafter, for each sample of Examples A1 to A9 and Comparative Examples A1 to A7 on which an cyan image had been formed, 10 sample sheets were put on top of another in such a manner that the surface with an image being formed thereon faced the surface of the dye-unreceptive layer (back surface). A smooth aluminum plate was put on each of the uppermost sheet and the lowermost sheet to sandwich the sample sheets between the aluminum plates. A load of 20 g·f/cm 2 was applied to the assembly from the top thereof. In this state, the assembly was allowed to stand in a constant-temperature oven at 50°C for 7 days. The migration of the dye of each sample to the back surface was visually inspected. Criteria for evaluation A: Little or no dye migration observed. B: Dye migration observed with no clear step pattern being observed. C: Dye migration observed with clear step pattern being observed. Sample under test Releasability of back surface of image-receiving sheet Stain resistance of back surface of image-receiving sheet Overall evaluation Ex. A1 x A Good Ex. A2 ○ A Good Ex. A3 ○ A Good Ex. A4 ○ A Good Ex. A5 ○ A Good Ex. A6 ○ A Good Ex. A7 ○ A Good Ex. A8 ○ A Good Ex. A9 x A Good Comp.Ex.A1 x B Poor Comp.Ex.A2 x B Poor Comp.Ex.A3 x C Poor Comp.Ex.A4 x B Poor Comp.Ex.A5 x B Poor Comp.Ex.A6 x B Poor Comp.Ex.A7 x C Poor The thermal transfer image-receiving sheet according to the present invention comprises a substrate sheet, a dye-receptive layer provided on one surface of said substrate sheet and a dye-unreceptive layer provided on the other surface of said substrate sheet, the dye-unreceptive layer comprising a composition composed mainly of at least one thermoplastic resin having at least one reactive functional group and an isocyanate compound or a chelate compound. The adoption of such a constitution brings the thermoplastic resin of the dye-unreceptive layer as a back surface layer of the image-receiving sheet to a crosslinked structure, which contributes to an improvement in heat resistance and a lowering in receptivity to a sublimable dye. This improves the suitability of the image-receiving sheet for automatic feed and delivery in a printer, and the stain of the back surface with a sublimable dye can be reduced even when a plurality of sheets are stored with the surface of the print facing the back surface. Further, in the thermal transfer image-receiving sheet according to the present invention, the thermoplastic resin of the dye-unreceptive layer as the back surface may be a thermoplastic resin having a hydroxyl group as the reactive functional group, more specifically, polyvinyl formal, polyvinyl acetoacetal or polyvinyl butyral. This embodiment enables the thermoplastic resin to be more surely reacted with the isocyanate compound or chelate compound, so that the above effect can be attained more efficiently and stably. Furthermore, in the thermal transfer image-receiving sheet according to the present invention, the dye-unreceptive layer provided in the back surface may further comprise an organic filler and/or an inorganic filler or a release agent, or an organic filler and/or an inorganic filler and a release agent. According to this embodiment, in addition to the above effect, a further improvement in releasability and slidability of the back surface of the thermal transfer image-receiving sheet can be attained. Further, since the release agent is fixed to the dye-unreceptive layer, it is not transferred to other places. Therefore, the suitability of the thermal transfer image-receiving sheet for automatic feed and delivery and the carriability in a printer can be further improved, so that the printing operation becomes stable. Furthermore, even though the thermal transfer sheet is fed into a printer with the back surface and the image-receiving surface of the image-receiving sheet being inversive and, in this state, printing is carried out, the sheet can be successfully delivered from the printer without the occurrence of heat fusing or sticking between the thermal transfer sheet and the back surface of the image-receiving sheet by heat. Furthermore, a further improvement in stain resistance of the back surface of the image-receiving sheet in the case of storage of a plurality of sheets with the surface of the print facing the back surface of the sheet can be attained. Thus, according to the present invention, a thermal transfer image-receiving sheet having a very excellent handleability can be easily provided.

Claims: A thermal transfer image-receiving sheet comprising a substrate sheet, a dye-receptive layer provided on one surface of said substrate sheet and a dye-unreceptive layer provided on the other surface of said substrate sheet, said dye-unreceptive layer comprising a reaction product of (a) at least one thermoplastic resin having at least one reactive functional group and (b) an isocyanate compound or a chelate compound. The thermal transfer image-receiving sheet according to claim 1 wherein said thermoplastic resin is a vinyl resin having at least a hydroxyl group. The thermal transfer image-receiving sheet according to claim 2 wherein the vinyl resin is polyvinyl formal, polyvinyl acetoacetal or polyvinyl butyral. The thermal transfer image-receiving sheet according to claim 1 wherein the reactive functional group of the thermoplastic resin is a hydroxyl group. The thermal transfer image-receiving sheet according to any one of the preceding claims wherein the dye-unreceptive layer further comprises an organic filler and/or an inorganic filler and/or a release agent. The thermal transfer image-receiving sheet according to claim 5 wherein the organic filler is nylon 12.

Inventors: KOMETANI SHINJI, SAITO HITOSHI, TAKAO SHINO, KOMETANI, SHINJI, SAITO, HITOSHI, TAKAO, SHINO, KOMETANI, SHINJI, C/O DAI NIPPON PRINTING CO.,LTD., SAITO, HITOSHI, C/O DAI NIPPON PRINTING CO.,LTD., TAKAO, SHINO, C/O DAI NIPPON PRINTING CO.,LTD.
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON PRINTING CO., LTD.
Application year: 1994
Main classification: B41M5
IPC codes: B41M5